The importance of host age and sex to the distribution of helminth parasites infecting free-ranging Yaku-Island macaques (Macaca fuscata yakui)

A fundamental principle in parasite ecology predicts aggregated distributions of parasites within host populations, which can be partly explained by host age and sex. As part of a longitudinal study of parasite ecology and health maintenance behaviour, a group of Yaku-island macaques (Macaca fuscata yakui) has been observed since December 2006. From October through November 2007, 39 individuals of Umi group were parasitized by 5 nematode species; Oesophagostomum aculeatum (87%, n=34), Streptopharagus pigmentatus (77%, n=30), Strongyloides fulleborni (28%, n=11), Gongylonema pulchrum (26%, n=10), and Trichuris trichiura (18%, n=7). An ANOVA showed that males (n=15) carried a higher mean species richness than females [n=25; F(1,32)=4.01, p=0.05], and that host age also influenced species richness [F(2,32)=7.2, p=0.003], with Tukey’s post-hoc tests [alpha=0.05] showing that juveniles (n=9) were infected by more species than both adults and sub-adults. Males also carried a higher mean eggs per gram of feces (EPG) than did females [F(1,184)=5.08, p=0.025] and though host age also influenced EPG [F(2,184)=3.02, p=0.05], Tukey's post hoc tests showed no significant differences between groups. Finally, there were no significant age and sex interactions for either species richness or EPG. These data support the idea that host age and sex can be important factors in the aggregated distribution of parasites within their host populations.